Earth has already a second moon, but a second sun is impossible. Right? Not quite.
In the constellation of Orion, Betelgeuse forms the left hand shoulder of the warrior (see the sword dangling from his belt). It is a red giant, a semi-regular variable star in the latter stages of its life whose apparent magnitude varies between 0.0 and 1.3. Which is a lot.
Will we ever live to see such a spectacle in the heavens? Scientists have calculated that the possibility of Betelgeuse imploding and exploding is somewhere between nil and a million years. As Betelgeuse lives a mere 640 light years away from earth, it might already have gone supernova 640 years ago.
So, keep watching the southern sky (if you live in the northern hemisphere).